So, I have a barebones version of MeeGo (barely) running on the Nexus S. I can't really do much with it on my own, but I'm posting the info here so you can build it and try it for yourself.
== What does n't work ==
I have my boot.img (kernel + ramdisk) and a MeeGo kickstart file at http://blog.steventroughtonsmith.com/2011/01/nexus-s-meego.html; you can use fastboot to boot the image, or flash it to the recovery partition to dual boot. The actual MeeGo rootfs is run from a rootfs.ext2 file you can drop onto the Nexus S using Mass Storage mode - no need for messy flashing or the like, you can thank me later).
There's not much else I can do on my own right now, so if you want to see anything become of this do get involved!
My kernel is Samsung stock; you will need to modify it to get X11 to run:
The only change was modifying the .config file to turn on CONFIG_VT (needed for X11, unless we recompile X11 without VT support).
Will add this to a newer kickstart, but for the time being, you can bring the brightness to full by doing: